Effects of gaseous emissions from the Namakwa Sands Mineral Separation Plant near Lutzville on the adjacent succulent Karoo vegetation : a pilot study

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(1)EFFECTS OF GASEOUS EMISSIONS FROM THE NAMAKWA SANDS MINERAL SEPARATION PLANT NEAR LÜTZVILLE ON THE ADJACENT SUCCULENT KAROO VEGETATION – A PILOT STUDY. BY. BEATRICE MK LUKAMA (Student No 14488590). Thesis presented in partial fulfilment of the requirements for the degree of Master of Ecological Assessment at the University of Stellenbosch. Supervisor: Prof SJ Milton (Department of Conservation Ecology) Co-supervisor: Dr C Boucher (Department of Botany and Zoology) Co-supervisor: Dr AT Botha (Private Consultant: Plant Physiology, Air Pollution). April 2006.

(2) DECLARATION. I, the undersigned, hereby declare that the work contained in this thesis is my own original work and that I have not previously in its entirety or in part submitted it at any university for a degree.. Signature:……………………………. Date:…………………….. i 2.

(3) ABSTRACT A pilot study was conducted at the Namakwa Sands Mineral Separation Plant, to investigate the effects of acidic gaseous emissions from the Mineral Separation Plant on the adjacent Succulent Karoo vegetation. Sulphuric acid fumes, a major gaseous emission of the mineral processing, was the subject of investigation of the present study, due to the potential high negative impact of elevated concentrations thereof on vegetation in the ecosystem. Permanent sample plots along three transects radiating from the Mineral Separation Plant were laid out in the eastern, south-eastern and southern directions following the prevailing wind directions and practical consideration of land accessibility. The ecological components assessed as indicators of possible pollution levels in the environment included percentage plant mortality, foliar sulphur content of selected plant species, chemical composition of solubles in mist and dust samples, and soil pH. In addition, the vegetation was screened for plant species suitable to be used as potential bioindicators. Potential bioindicator plant species were selected on the basis of their relatively wide distribution in the study area and apparent sensitivity to the ambient air pollutants. The percentage of dead plants of each species that occurred on the sample plots was used as a criterion of the possible sensitivity of the plant species towards air pollution. The bioindicator plant species selected for potential monitoring purposes were: Galenia fruticosa, Lampranthus suavissimus, Lycium ferocissimum and a Ruschia sp. (SP 9). Plant mortality was greater nearer the emission source, with 28 + 5 % dead plants at 400 m, 19 + 6 % at 800 m and only 10 + 4 % at 1,200 m from the Mineral Separation Plant. Data summed for all species recorded and pooled for all three transects per sampling distance. With the methods used in this study, in the case of all sample plots on the three transects, no significant difference was found between the mean pH values of soil samples collected from open spaces without plant cover (8.01 + 0.46) and those collected underneath shrubs (8.91 + 0.96). Subsequently only the pH values of soil samples collected on open spaces were used to investigate the variation in soil acidity with distance and direction from the emission source. The means represent total number of samples from open space versus those collected from underneath shrubs. ii. 3.

(4) The pH of soil samples increased with distance from the emission source along the transects to the south and south-east of the emission source. Eastward of the emission source, soil pH values remained relatively low at all sample distances. This pilot study could not determine whether the continuous acidity of the soil along the eastern transect in the direction of the prevailing wind, was caused by increased deposition of gaseous emissions on the higher lying hilly terrain in this area, or by the underlying geology. Ion chromatographic analysis of mist and dust samples collected on each sample plot indicated the presence of several chemicals that had probably originated from the gaseous emissions from the Mineral Separation Plant as well as wind blown constituents from the adjacent surroundings of the sample plots. Of these chemicals, only the sulphate concentrations of the mist and dust samples were further evaluated, since that could be related to the emission of sulphuric acid fumes by the Mineral Separation Plant. Results indicated that the mean sulphate concentration of mist and dust samples collected from sample plots relatively close to the Mineral Separation Plant, 118.8 + 31.6 mg/litre (400 m), were higher than further afield, decreasing to 57 + 30.1 mg/litre at 800 m and 43.1 + 19.6 mg/litre at 1,200 m. These values, representing the mean sulphate concentrations of mist and dust samples at each sampling distance (data of the three transects pooled), differ significantly at the 85 % confidence level. Statistical evaluation of the data of the mist and dust pH measurements, pooled for the three transects on the basis of distance, indicated a gradual increase of the mean values from 400 m (7.3 + 0.26), through 800 m (7.7 + 0.34), to 1,200 m (8.2 + 0.83), although these values were not significantly different. A decreasing trend in accordance with that in the case of the sulphate concentrations of mist and dust samples with distance from the mineral processing plant, was also observed in the sulphur content of the leaves of selected plant species, with mean sulphur content higher at 400 m sampling distance (0.29 + 0.091 %) than at 800 m (0.264 + 0.086 %) and a further decline at 1,200 m (0.232 + 0.079 %), data of the three transects pooled. However, these values were also not significantly different.. iii. 4.

(5) Although not significantly so, the decreasing trend in the results of the sulphate concentration of mist and dust samples, the sulphur content of plant leaf samples as well as plant mortality observed, and increasing soil pH values with distance from the Mineral Separation Plant, suggest that the gaseous emissions from the Mineral Separation Plant could probably have had a detrimental effect on the adjacent Succulent Karoo vegetation. A more detailed study is necessary to confirm this trend. In addition it is recommended that in order to clarify the soil pH measurements outcome along the eastern transect that were contradicted by the results of the mist and dust pH measurements, a more intensive survey over a greater distance (at least further than 1.2 km from the Mineral Separation Plant), be conducted to quantify vegetation damage and acid deposition to the east of the emission source.. iv 5.

(6) UITTREKSEL 'n Voorlopige studie is naby die Namakwa Sands Mineraalskeidingsaanleg onderneem om die invloed van suur gas-vrylatings vanaf die aanleg op die aanliggende Sukkulente Karoo plantegroei te ondersoek. Swaelsuurdampe, 'n belangrike gas-vrylating vanaf die mineraalskeidingsproses wat potensieel 'n ernstige negatiewe invloed op plantegroei in die ekosisteem he, was die spesifieke onderwerp van die huidige studie.. Permanente proefpersele is in drie transekte vanaf die mineraalskeidingsaanleg uitwaarts, in die oostelike, suid-oostelike en suidelike rigtings uitgelê. Hierdie rigtings is gekies na aanleiding van die heersende windrigtings, asook praktiese oorwegings rondom die toeganklikheid van die area.. Die volgende ekologiese komponente is as indikatore van moontlike besoedelingsvlakke in die omgewing geasseseer: persentasie plantsterftes, die swaelinhoud van die blare van sekere plantsoorte, die chemiese samestelling van opgeloste stowwe in mis- en stofmonsters en die pH van die grond. Daarbenewens is die plantegroei ook deursoek vir plantsoorte wat as potensiële bio-indikators gebruik kan word.. Plantsoorte met 'n relatief wye verspreiding in die studiegebied en wat skynbaar sensitief teenoor die teenwoordige lugbesoedeling vertoon het, is as potensiële bio-indikators gekies. Die persentasie dooie plante van elke spesie wat op die proefpersele voorgekom het, is as kriterium van moontlike sensitiwiteit van die plantsoort teenoor lugbesoedeling gebruik. Die plantsoorte wat hiervolgens as bio-indikators geselekteer is om vir potensiële moniteringsdoeleindes gebruik te word, was: Galenia fruticosa, Lampranthus suavissimus, Lycium ferocissimum and a Rushia sp. (SP 9). Meer plantsterftes het op die persele nader aan die vrylatingsbron voorgekom, nl. 28 + 5 % dooie plante op 400 m, 19 + 6 % op 800 m, en slegs 10 + 4 % op 1,200 m vanaf die mineraalskeidingsaanleg (data van alle plantsoorte is bymekaargetel en die van al drie transekte per monsterings-afstand is saamgegroepeer).. Met die metodes wat in hierdie studie gebruik is, kon geen statisties betekenisvolle verskil tussen die gemiddelde pH-waarde van grondmonsters wat op al die persele en transekte, op oop terrein sonder plantbedekking (8.01 + 0.46) en dié wat onder struike versamel is (8.91 + 0.96), aangedui word nie. Vervolgens is slegs die pH-waardes van grondmonsters wat op oop terrein versamel is, in ag geneem vir 'n ondersoek van die variasie in grondsuurheid met afstand en rigting vanaf die vrystellingsbron. v 6.

(7) Die pH van grondmonsters geneem vanaf die proefpersele op die transekte suid en suid-oos vanaf die mineraalskeidingsaanleg het met afstand vanaf die aanleg toegeneem. Ten ooste van die vrylatingsbron het die grond pH waardes op alle monsteringsafstande relatief laag gebly. Hierdie voorlopige studie kon nie vasstel of die volgehoue relatiewe suurheid van die grond wat langs die oostelike transek in die rigting van die heersende wind gemeet was, deur moontlike verhoogde neerslag van gasvrylatings op die hoër liggende heuwels veroorsaak was en of dit moontlik 'n gevolg van die onderliggende geologie van die area is nie.. Ioonchromatografiese analise van mis- en stofmonsters wat vanaf elke perseel versamel is, het die teenwoordigheid van verskeie chemikalië aangedui wat vermoedelik vanaf die mineraalskeidingsaanleg, sowel as windgedrewe stowwe van die omliggende omgewing, afkomstig kon wees. Van hierdie chemikalië is slegs die sulfaat konsentrasies van die mis- en stofmonsters verder ge-evalueer, aangesien dit waarskynlik met die vrylating van swaelsuurdampe vanaf die mineraalskeidingsaanleg verbind kon word. Die gemiddelde sulfaatkonsentrasies van monsters vanaf proefpersele relatief na aan die mineraalskeidingsaanleg (400 m), was hoër (118.8 + 31.6 mg/l) as verder weg,waar dit afgeneem het na 57.0 + 30.1mg/l by 800 m en 43.1 + 19.6mg/l by 1,200 m vanaf die aanleg. Hierdie waardes (data van die drie transekte saamgevoeg), kan met 85 % sekerheid as betekenisvol verskillend beskou word.. Data van die bepalings van die suurgehalte van die mis- en stofmonsters wat vir die drie transekte per afstand van die proefpersele vanaf die mineraalskeidingsaanleg saamgevoeg is, het aangetoon dat daar 'n geleidelike toename in die gemiddelde pH waardes van 7.3 + 0.26 (400 m), tot 7.7 + 0.34 (800 m) en 8.1 + 0.83 by 1,200 m was, alhoewel hierdie toenames nie betekenisvol was nie.. 'n Ooreenstemmende afnemende neiging as wat vir die sulfaatkonsentrasies in mis- en stofmonsters met afstand vanaf die aangleg waargeneem is, is vir die swaelvlakke in die blare van geselekteerde spesies waargeneem. Die gemiddelde swaelinhoud van blaarmonsters geneem 400 m vanaf die aanleg was hoër (0.290 + 0.091 %) as die geneem op 800 m (0.264 + 0.086 %), met 'n verdere afname in die geneem op 1,200 m (0.232 + 0.079), data van die drie transekte saamgevoeg. Hierdie waardes was egter ook nie betekenisvol verskillend nie. vi 7.

(8) Alhoewel nie betekenisvol nie, dui die dalende neiging van die sulfaatkonsentrasies in mis- en stofmonsters, die swaelinhoud van blaarmonsters, en die persentasie plantsterftes, asook die toename in grond pH met afstand vanaf die minderaalskeidingsaanleg, aan dat die suur gasvrylatings deur die aanleg moontlik 'n skadelike invloed op die aanliggende sukkulente Karoo plantegroei kan hê. 'n Meer intensiewe studie is nodig om hierdie neigings te bevestig. Verder word aanbeveel dat, ten einde die weersprekende resultate van die grond pH metings en die pH metings van mis- en stofmonsters ten opsigte van die oostelike transek uit te klaar, 'n meer omvattende opname oor 'n groter afstand (minstens verder as 1 km vanaf die aanleg) uitgevoer word om skade aan die plantegroei sowel as suur neerslag ten ooste van die vrylatingsbron te kwantifiseer.. vii 8.

(9) ACKNOWLEDGEMENT The pilot study research was supported by Namakwa Sands Mine (Pty) Ltd in partnership with Technology Human Resource Industrial Programme, Project 2645 “Arid mine-spoil biodiversity enhancement” of the Department of Conservation Ecology, University of Stellenbosch. My appreciation is directed to these organizations for their genuine concern for sustainable development. My appreciation goes to Mr T Hälbich and Ms N Marx of the Environmental Management Section, Namakwa Sands Mine, for providing information about the operations at the Namakwa Sands Mineral Separation Plant. I wish to express my appreciation to Mr WP de Clercq of the Soil Science Department, University of Stellenbosch, for providing assistance with the acquisition of the Modified Wilson and Cooke (MWAC) samplers used in collecting mist and dust samples and the subsequent chemical analysis of these samples. I thank Mr M Gordon of the Soil Science Department, University of Stellenbosch, for assistance with ion chromatographic analysis of the mist and dust samples. Thanks to Dr M Kidd of the Statistics Department, University of Stellenbosch, for guidance with the statistical analysis. In all these Glory and honour is due to the almighty God for providing me with such supervisors, Prof SJ Milton, Dr C Boucher and Dr AT Botha, who worked so hard to guide my research work so that I can obtain a useful product. I thank my husband Mark for the encouragement, together with my children Chileshe, Mubanga and Sipiwe for enduring my absence from home.. viii 9.

(10) ITEM. PAGE No. DECLARATION…………………..…………..…………………………………………….………...i ABSTRACT............................................................................................................................................ii OPSOMMING…………………….…………………………………………………..…….………...v ACKNOWLEDGEMENTS................................................................................................................viii TABLE OF CONTENTS CHAPTER 1: GASEOUS EMISSIONS AND THE EFFECTS ON VEGETATION…….…….…9 1. Introduction and background to study……...................................................................................9 1.1 Introduction………….…………………………………………………………………………..…..9 1.2 Location and the topography of the study area.……........................................................................12 1.3 Geology of the study area………………………….………………………………………………14 1.4 Sources of pollution in the study area………………………….…………………………………..14 1.4.1 Mineral processing procedure………………….………………………………………..…...15 1.5 Meteorological conditions of study area...........................................................................................17 1.5.1 Wind pattern …………………………………………………………….…………………...18 1.5.2 Temperature and rainfall…………………………………………..........................................20 1.6 Vegetation of the study area.……....................................................................................................21 1.7 Research objectives………….………………………………………………………….……….…24 CHAPTER 2: LITERATURE REVIEW ON ACIDIC GASEOUS EMISSIONS, AND THE EFFECT ON VEGETATION…………………..……………………………………….…………..26 2.1 Acidic gaseous emissions and the effects on vegetation……...………..…….................................26 2.1.1 Sulphur dioxide as an air pollutant....……………...……………...........................................27 2.1.2 Vegetation assessment …………………………………………………………...….……....29 2.2.2.1 Selection of potential bioindicator plant species……………………….……….…30 2.2 Pollution effects on soil…………………...…..…………...……………...…………………….…32 2.2.1 Soil acidity…………..………………………………………………...…..….………….…..33 2.2.2 Electrical Conductivity………………………………………………………...…….…........35 2.3 Measurement of mist and dust deposition………………………..……….……………….…........36 2.4 Foliar sulphur content……....…………….…..……………………..…………………….…...…..38 2.4.1 Sulphur metabolism……………………...………………………………....………..………39 CHAPTER 3: METHODS USED TO ASSESS THE VEGETATION AND TO CONDUCT THE CHEMICAL ANALYSIS OF THE SOIL, PLANTS MATERIALS AND MIST AND DUST SAMPLES...………..…………………………………..………………………………...….. 41 3.1 Assessment methods..………………………………..……..……………………………….……..41 3.1.1 Research approach…...……………………………...………………………..………….…..41 10.

(11) 3.1.2 Vegetation assessment..……………………………………...………………..………..……42 3.1.2.1 Field sampling methods………………………………..…………...……….……..42 3.1.2.2 Scanning for potential bioindicator plant species………………...…….……...…..45 3.1.3 Statistical analysis…………………………………………………….…….……….….……45 3.1.3.1 Canonical Correspondence Analysis………………………………….…….……..46 3.1.3.2 Clustering analysis..……………………………………………………….….……46 3.2 Soil sampling……………………………..…………………………………...…………….……..47 3.2.1. Field methods…………………………………………………………….……………...…..47 3.2.2 Laboratory procedure for pH analysis………………………………………..…..….….…...49 3.2.3 Statistical analysis…………………….………………………………..……………...……..49 3.3 Mist and dust capture and chemical analysis.……………………………..….….…………….…..50 3.3.1 Field methods………………………………………………………………….…………......51 3.3.2 Laboratory methods…………………………………………………………….….…….…..52 3.3.3 Ion chromatographic process……...…………………...………………………....……….…52 3.3.4 Statistical analysis………………………….……………………………………...……..…..53 3.4 Plant foliar sulphur content……………………………...…………………...……...….…..….…..53 3.4.1 Field methods..………………………………………………………………...…….…...…..56 3.4.2 Laboratory methods………………………………………………………….…………..…..56 3.4.2.1 Inductively Coupled Plasma Atomic Emission Spectroscopy...……………....…...57 3.4.3 Statistical analysis…………………………………………………….………………….…..58 CHAPTER 4: RESULTS….……………………..….………………………………...…..…………59 4.1 Vegetation assessment ……..…………….......................................................................................59 4.1.1 Scanning for potential bioindicator plant species ……...…..………..……………….……...61 4.1.2 Canonical Correspondence analysis.……..……………….…………………….…….……..62 4.1.3 Clustering analysis ……...………………..………………………………………….………64 4.2 Soil sampling and chemical analysis…………………....................................................................65 4.2.1 Descriptive statistics………………………………….……………………………….……..65 4.2.2 Paired t-test…………………………………….…………………………………….………65 4.2.3 Repeated Measurements Analysis of Variance……………………………………..…..……67 4.2.4 Contour map for soil pH………………………………….…………………….…….……...69 4.3 Mist and dust survey….……... …………………………..……………………………..…….…...73 4.3.1 pH results……………………………………………………………………...…..…….…...73 4.3.1.1 Pearson correlation……………………………………………….…….….….……75 4.3.2 Electrical Conductivity ……..…………………………………………………….……..…..76 4.3.2.1 Two-way ANOVA for electrical conductivity results………………….……...…..77 4.3.3 Mist and dust sulphur concentration……………...……………………………..……..….....79 4.3.3.1 Descriptive statistics.………………………………………………………………...……80 4.3.3.2 Two-way ANOVA for sulphur concentration ……………….….…………....…...80 4.4 Plant foliar sulphur content………... ………………….……………………………………...…...82 CHAPTER 5: DISCUSSION, CONCLUSIONS AND RECOMMENDATIONS……..….……...85 5.1 Discussion………………………………………..………………...…………………….….……..85 5.1.1 Vegetation assessment ………….…………………………………….…………….….……86 5.1.1.1 Potential bioindicator plant species ………………………………………..……...87 5.1.1.2 Integrated approach…………………………………………….……….…….……89. 11.

(12) 5.1.1.2.1 Canonical Correspondence Analysis…………...………….….…………89 5.1.1.2.2 Clustering Analysis………….……………………………………….…..91 5.1.2 Soil responses…………….………………….……………………………….………….…...92 5.1.3 Mist and dust responses………...………………..…………………………………….….…94 5.1.3.1 Mist and dust electrical conductivity………...….…………………………....…....94 5.1.3.2 Mist and dust sulphur concentration………………. ……………………....……...95 5.1.4 Foliar chemical responses..……………...………………………………………...………....95 5.2 Conclusions……………………..……………………………………………………………….…97 5.3 Recommendations……………..…………………………………………………….….……….…98 6. REFERENCES................................................................................................................................100 APPENDICES Appendix 1: Chemical content of the windblown dust from soil and gaseous emissions from the Namakwa Sands Mineral Separation Plant as analysed from mist and dust samples........115 Appendix 2: Pictures taken from the eastern side of the Namakwa Sands Mineral Separation Plant showing the effect of the predominant westerly winds………….………….………........116 Appendix 3: Plant abundance and mortality per species…..………………………..…....…....…….116 Appendix 4: Location of permanent sample plots at the Namakwa Sands Mine Mineral Separation Plant……..…………...……...…………………………………………………..…..…….120 Appendix 5: Plant abundance, crown cover and proportion of dead plants per sample plot.….…....125 Appendix 6: Plant samples location points……………………....…….…………….…….…….…..127 Appendix 7: Multivariate analysis data matrix..………………….………………..……...…….…...131 Appendix 8: Mist and dust sample chemical analysis results…….…………….……..………….….132 Appendix 9: Plant foliar samples drying process data and the sulphur content results………....…...133 Appendix 10: Plant distribution trend for Transects A, B and C with distance from the gaseous emission source and the trend of the proportion of the dead plants along the transects....134 Appendix 11: Soil analysis data for open space (O) and from underneath the shrubs (S)...….…..…136 Appendix 12: pH measurements of soil samples for contour map……………....….……..……..….138 Appendix 13: Location of the transects on Namakwa Sands Mineral Separation Plant contour map......................................................................................................................................142 Appendix 14: Pictures of selected plant species from the Namakwa Sands Mine Mineral Separation Plant area……………………………….………………..………………………..……..143. 12.

(13) LIST OF FIGURES Figure 1.1: Conceptual framework……………………………………………….…………...……....12 Figure 1.2: Map showing the position of Lützville on the Western Cape Coast………………...…....13 Figure 1.3: Flow chart of mineral processing at Namakwa Sands Mineral Separation Plant….…......16 Figure 1.4: Wind rose for winter, autumn, summer and spring……………………………….………19 Figure 1.5: Position of the Succulent Karoo Biome in relation to the other biomes of South Africa...21 Figure 1.6: Vegetation map of the western Cape coast supporting Strandveld vegetation…...……....23 Figure 2.1: Release of gaseous emissions from the Namakwa Sands Mineral Separation Plant…..…27 Figure 3.1: Layout of permanent sample plots in the pilot study….……..……………………..…….44 Figure 3.2: Location of soil sample points…..…………..………….………………………..……….48 Figure 3.3: Construction scheme of the Modified Wilson and Cooke mist and dust sampler and the Modified Wilson and Cooke sampler as set in the sample plots….…………….……..……..51 Figure 3.4: Pictures of damage observed on plants………………….………..………………..……..55 Figure 4.1: Histogram of plant frequency and proportion of dead plants…………….………………60 Figure 4.2: Scatter plot for the number of dead plants……………………...…………………..…….61 Figure 4.3: The Canonical Correspondence Analysis diagram……….……..………………..……....63 Figure 4.4: The clustering Analysis diagram…….…………...………………………………..….…..64 Figure 4.5: Effect of the open space and shrub canopy on the soil pH………………...……..……....68 Figure 4.6: Effect of distance on soil pH for open space and underneath the shrubs………....……....69 Figure 4.7: Soil pH contour map…………..…………………………………………………..….…..70 Figure 4.8: Soil pH trends for Transects A, B and C………………..…………………………….…..71 Figure 4.9: Soil pH variation with altitude…………………..…………………………………….….71 Figure 4.10: Graphs showing altitude variation with distance……………..……………...……….…72 Figure 4.11: Histogram for soil pH gradient….……………...…..………….…………………….…..73 Figure 4.12: Comparison of the mist and dust pH for the pooled data….…………..…………….…. 75 Figure 4.13: Histogram for electrical conductivity…………..…………………………………….….77 Figure 4.14: Effect of direction and distance on electrical conductivity……..…..…………………...78 Figure 4.15: Effect of direction on electrical conductivity……..……………..……………………....78 Figure 4.16: Effect of distance on electrical conductivity……………..………..………………….....79 Figure 4.17: Effect of direction and distance on sulphur concentration in mist and dust……...….….81 Figure 4.18: Effect of transects on sulphur concentration in mist and dust…………..…....……....….81 Figure 4.19: Effect of distance on sulphate concentration in mist and dust…………...……………...82 13.

(14) LIST OF TABLES Table 4.1: Summary of the total number of plants and the proportion of the dead plants……....….....59 Table 4.2: Univariate test of significance for total number of dead plants…..…...…………………...60 Table 4.3: Selection of potential bioindicator plant species……......……………………………..…..62 Table 4.4: Descriptive statistics of the pH values for the open space and sub-shrubs……..…..…...…65 Table 4.5: The paired sample test of the pH values for the open space and sub-shrubs……..….….....67 Table 4.6: Descriptive statistics for mist and dust pH values………..…….………………………….74 Table 4.7: Pearson correlation analysis for pH and distance………..…….…………...…………...…76 Table 4.8: Descriptive statistics………………...……………...……………………………………...80 Table 4.9: Plant foliar sulphur content…………………………...………...…………………..……...83. 14.

(15) CHAPTER 1: GASEOUS EMISSIONS AND THE EFFECTS ON VEGETATION _________________________________________________________________________________. 1.. INTRODUCTION AND BACKGROUND TO STUDY AREA 1.1 Introduction Atmospheric emissions from industries do not only affect the balance of gases in the atmosphere, they also cause environmental pollution on the earth's surface. These result in deleterious effects that can endanger human health, harm living resources, or upset the amenities or other legitimate use of the environment (Reeves 1996). Fifield and Haines (2000) contend that air pollutants can be divided into two categories. The first consists of pollutants that can change their chemical composition on reaction with radiation or other atmospheric elements to form a secondary pollutant. According to Dässler and Börtitz (1988) secondary pollutants are formed in the atmosphere by the mutual reaction with vapour, under the influence of sunlight, or by oxidation and condensation. The second category consists of stable primary pollutants that remain unchanged in the atmosphere and are consequently comparatively easily traced to their source. The primary pollutants normally arise from industrial, commercial, domestic transport, agricultural activities and are in the form of dust, smoke, fumes and droplets (aerosols). Radiative heat loss can affect the temperature and concentration of the pollutants to change their chemical composition (Zhu and Gore 2005) Air movement determines the transportation of the emissions in the atmosphere. The effect of the pollutants in the emissions depends on their persistence and lifespan and can either be local or global (Torvela 1994). Some of the chemical elements occur naturally in the environment. However, in polluted areas their concentrations tend to rise to lethal levels, gradually killing organisms. Hence, the decline in diversity and species richness is usually the first indication of pollution effects in an environment (Begon et al.1996). The mining of heavy minerals in the Succulent Karoo by Anglo American Corporation’s Namakwa Sands Mine, is an important undertaking for the economic development of South Africa. In South Africa strip-mining is expanding in the arid winter rainfall areas of the country and although this is economically important and a provider of employment and training for local people, it has a detrimental effect on vulnerable biological diverse environments where vegetation growth is 9.

(16) restricted by aridity, wind and nutrient-poor soils (Milton 2001). With this kind of venture we must not forget that South Africa is committed to sustainable development, so that the development process should not be done at the expense of the environment and of future generations. This is in accordance with the National Environmental Management Act (NEMA, Act No 107 of 1998), which stipulates that development must be sustainable. This calls for an urgent action to formulate approaches to combat ecological habitat destruction and promote sustainable development. There is a limit to which any company can be allowed to release emissions into the atmosphere (Manly 1997, Milton 2001). The present study provides recommendations to promote ecosystem conservation. Despite the economic justification for establishing the Mineral Separation Plant, environmental management requirements have to be considered. Economic theories do not inform us about what should be done to alleviate pollution problems (Field and Field 2002). Scientific research provide a framework in which, if sufficiently useful information is obtained, a decision can be reached that is based on an impartial view of the consequences of environmental pollution (Burrows 1979). The results of this pilot study could be used as a basis for monitoring the effects of the gaseous emissions on the vegetation around the Namakwa Sands Mineral Separation Plant.. The Namakwa Sands Mineral Separation Plant emits gaseous substances that could be having negative effects on the adjacent Succulent Karoo vegetation. To alleviate this problem Namakwa Sands Mine management has been making efforts to ensure that the potential effects of the gaseous emissions on the surrounding ecosystems are monitored. “The responsibilities of the mining industry pertaining to environmental management stems mainly from the requirements of the Minerals Act, 1991, that is administered by the Department of Minerals and Energy. Other legislation, such as the Environment Conservation Act of 1989, the Water Act of 1956, and the Atmosphere Pollution Prevention Act of 1965, play an important role in the management philosophy” (Namakwa Sands 2002).. An adaptive approach to ecosystem management is vital. Adaptive management consists of four basic components: monitoring, assessment, decision making and implementation of the programme (Jensen and Bourgeron 2001). Hence, explicitness and clarity of ecosystem management goals and principles need to be recognised. The interaction of ecological, socio-economic, political and institutional perspectives has an effect on biodiversity conservation. Decisions should be based on the clear understanding of the total pollutant movement and effects on the environment (McCormac 10.

(17) and Varney 1971). Air pollutants are transported by wind and transformed into other species by radiation. This pilot study will provide information on the characteristics of the pollutants from the Mineral Separation Plant and their effects on the surrounding vegetation.. The present pilot study is directed towards providing baseline information on a) plant species composition b) present condition of plant communities and c) whether present/past emissions can be readily quantified. The study was carried out along 3 transects, within 1,200 m radius from the Namakwa Sands Mineral Separation Plant. The identification of potential indigenous bioindicator plant species for monitoring the effects of any contamination on a long-term basis will assist in avoiding the exceeding of critical pollution levels. This pilot study endeavours to put into context the interactions between various ecological components which include: soil pH, wind direction, mist and dust sulphate concentration, topography and possible effects of the gaseous emissions on the vegetation (Figure 1.1). It should be remembered that the investigation of atmospheric air pollutants is complex and multidisciplinary by nature (McCormac and Varney 1971). Meffe and Carroll (1997) emphasised that biodiversity conservation is not just species diversity conservation, but that it must address multiple levels of organisation at various spatial and temporal scales. The pilot study provides ecological approach to evaluating the effects of emissions from the Mineral Separation Plant on the surrounding vegetation. Ecophysiological reactions of plants in response to environmental stimulus provide the fundamental basis for the use of the indicator properties found within the ecosystems (Zonneveld 1982). In the present study area, there is a dumping ground for the mineral processing by-products in the eastern direction, about 500 m from the Mineral Separation Plant. These are in the form of loose dust that is constantly blown into the surroundings and has the potential of affecting the soil pH investigations due to their iron content. During the present study an attempt was made to identify potential plant bioindicator species. This approach is required, because Namakwa Sands Management is concerned about both the functional aspects of the ecosystem as well as the potential effects of the present levels of gaseous emissions on the ecosystem. Apart from the presence of the toxic pollutants, it is essential to consider the abiotic environmental factors such as precipitation and topography and the biotic factors such as plant mortality, crown density and herbivory, in each particular ecological assessment scenario. Biotic/abiotic factors have potential biological effects and could influence bioindication (Schebert 1982).. 11.

(18) Figure 1.1: Flow chart of the important ecological components evaluated to aid in the identification of potential plant bioindicator species during a pilot study at the Namakwa Sands Mine Mineral Separation Plant and to determine the effects of the gaseous emissions on vegetation.. Potential acid fume pollution is present in the area and this requires assessing. The Namakwa Sands Mineral Separation Plant, through the processing of the various heavy minerals, emits acidic fumes into the atmosphere. The wind rose data suggests that the emissions are blown eastwards, from the Mineral Separation Plant by the prevailing westerly winds. Experimental sites immediately to the east of the Mineral Separation Plant were selected for this pilot study. The control sample plots could not be established in the western direction of the Mineral Separation Plant, because the area is reserved for depositing radio active materials that result from processing the minerals.. 1.2 Location and topography of study area The study area is in Succulent Karoo vegetation adjacent to the Namakwa Sands Mine Mineral Separation Plant, a heavy mineral processing plant located relatively close to the north western coast of the Western Cape Province, South Africa (Figure 1.2). The Mineral Separation Plant is 60 km south-east of the open strip mining area, about 10 km south of Koekenaap a small village to the north-west of Lützville, and about 300 km north of Cape Town (De Villiers et al. 1999). The study 12.

(19) area covers approximately 1.12 km2 to the immediate east and south of the Mineral Separation Plant. The Mineral Separation Plant is situated within the Jaagleegte River valley, which, according to Desmet and Helme (2003) forms the boundary between two distinct types of the south Namaqualand vegetation, namely Sandveld and Knersvlakte. The topography is undulating punctuated with a number of hills. According to Cowling and Hilton-Taylor (1999) the geographical gradients around the Mineral Separation Plant are considered a unique feature of this environment.. Figure 1.2: Location of the Namakwa Sands Mineral Separation Plant near Lützville, Western Cape Province, South Africa. Stations 1 and 3 are the local weather stations for Namakwa Sands Mine. Weather station 2 is situated in the Cape Peninsula (Struthers and Watt 2001). 13.

(20) 1.3 Geology of the study area The western Cape coast has predominantly granitic catchment soils, with pan water evaporation that leads to precipitation of calcite, dolomite, gypsum and halite a markedly stratigraphic progression in pan sediments (Smith and Compton 2004). Around the Mineral Separation Plant there are quartz patches that are acidic in higher elevations and saline at the bottom of slopes (Desmet and Helm 2003).. 1.4 Sources of pollution in the study area Industrial emission sources utilise various inputs and apply different types of technologies in production and consumption. During the industrial operation process residuals are produced, whose handling has a critical effect on ecosystems (Field and Field 2002). The Mineral Separation Plant uses sulphuric acid (H2SO4) to allow effective electrostatic separation of the mineral particles. This involves hot acid leach treatment of zircon and rutile ore to strip off the magnetic iron coating. Apart from the production of minerals, this treatment supposedly result in the emission of acid fumes of sulphate (SO4=), fluoride (F-), chloride (Cl-), nitrate (NO3-), phosphate (PO4=) and bromine (Br-), are released into the atmosphere via two smoke stacks, as was evident from the mist and dust samples chemical analysis. These emissions are likely to affect the biodiversity downwind, as plant wilting had been observed in patches around the Mineral Separation Plant (Hälbich 2004, pers. Comm.). This served as the rationale for Namakwa Sands management to facilitate research into the local effect of the acidic gaseous emissions on the adjacent vegetation.. Hälbich T- Environmental Management Manager, Namakwa Sands Mine (Pty) Ltd, Saldanha.. 14.

(21) The present study was launched to provide preliminary information on the effect of the sulphuric acid fumes (H2SO4) on the vegetation around the Mineral Separation Plant. These fumes are emitted from the hot acid leach treatment. The present investigation is based on the apparent acid output produced by two of four smoke stacks at the plant. Our investigation uses the finding that two of the four stacks, which are about 80 m apart and 100 m height, yield different amounts of H2SO4 emissions. Stack A (North) yields 3 μg/m3/s and stack B (South near the railway line) yields 4.2 μg/m3/s according to a survey conducted in 2003 (Hälbich 2004 pers. Comm.). The smoke stacks have been constructed with a height well above the other structures to facilitate the release of the gaseous emissions into the atmosphere, to reduce the effect of the pollutants in the immediate surrounding. 1.4.1 Mineral processing procedures Anglo American Corporation under the subsidiary name of Namakwa Sands owns approximately 14,992 hectares of land, within the Western Cape Province. Currently the mining operations relevant to this study are taking place in an area of approximately 4,700 hectares. Open cast mining is used to remove mineral-rich sands from which the heavy minerals ilmenite, rutile and zircon are extracted. The operational area is divided into two separate sectors, Graauwduinen east with approximately 3,370 hectares and Graauwduinen west with approximately 1,400 hectares (EEU 1990). The Primary Concentration Plant (PCP) is the West Section of this mine. In this section the total heavy mineral, of typically 15% content percent of volume is concentrated by a gravity separation method to 90% total heavy mineral concentrate. This product is then sent to the Secondary Concentration Plant (SCP), situated at a distance of about 60 km. The SCP was commissioned in 1994, principally to mineralise the magnetic (ilmenite) from the non-magnetic (zircon, rutile and leucoxene) products (Namakwa Sands 2002).. Hälbich T- Environmental Management Manager, Namakwa Sands Mine (Pty) Ltd, Saldanha.. 15.

(22) Figure 1.3: Flow chart to illustrate the material flow from inputs to the outputs in the Mineral Separation Plant. (source: Hälbich 2004 pers. Comm.).. The magnetic and non-magnetic minerals are then sent to the Mineral Separation Plant (Figure 1.3). One of the activities conducted at the Mineral Separation Plant is to process the magnetic stream to produce an ilmenite stream, while the non-magnetic stream is processed into rutile and zircon for the export market. The ilmenite is transported to the smelter and titanium dioxide slag is produced, leaving sulphate and iron slag as by-products (Namakwa Sands 2002). The purification of rutile and zircon by stripping off the iron coating requires the application of a hot acid leaching treatment (sulphuric acid leach, 40% H2SO4, 23 gram H2SO4/liter, at reactor temperature of 150o C input and 85oC output). It is from this process that the acid fumes are emitted to the atmosphere (Hälbich 2004 pers. Comm.). In metal industries, such as that conducted by Namakwa Sands Mine (Pty) Ltd, the most important emissions of environmental concern are of sulphur dioxide (SO2) and particulates (Jacobson 2002). Hälbich T- Environmental Management Manager, Namakwa Sands Mine (Pty) Ltd, Saldanha.. 16.

(23) During the production process of some non-ferrous metals, the oxidation of sulphide concentrates raises the concentration of SO2 in the emissions (Torvela 1994). The procedure of handling residuals has a critical impact on subsequent stages, as some residues can be recycled, while others can be treated to render them benign on emission (Field and Field 2002). Apart from the release of sulphur dioxide from the Mineral Separation Plant, in the gaseous emissions, there are additional chemical compounds released from other operations that take place at the Mineral Separation Plant (Appendix 1). These chemical compounds includes; F-, Cl-, NO3-, PO4= and Br- found in the mist and dust captured from the study area.. 1.5 Meteorological conditions of the study area With air pollutants there is no uniform distribution path. The mixture of gases is affected by constant dynamic changes with vast quantities being added or removed from the atmosphere by various natural and industrial processes (Lyons and Scott 1990). According to McCormac and Varney (1971) it is necessary to consider meteorological as well as topographical factors when assessing air pollution. The meteorological and topographical factors have an influence on the dynamics of the gaseous emissions in the atmosphere. Air pollution meteorology focuses on the destiny of these pollutants once emitted into the atmosphere (Lyons and Scott 1990). Once the gases are released into the atmosphere they undergo transportation, dispersion, transformation and deposition. Samson (1994) indicated that, the capacity of the atmosphere to absorb gaseous emissions from a point source depends on the mechanisms of pollution transportation, dilution and dispersion.. The average wind transports the pollutants away from the source, whereas dispersion results from the turbulent characteristic of the atmosphere to diffuse the pollutants in various directions (Lyons and Scott 1990). Disturbances of the energy balance of the atmosphere are caused by the rapid heating of the earth’s surface in comparison to the water body (Samson 1994). The heated air rises giving a localised low pressure system over the landmass. This leads to the flow of air from a high pressure cell over the water body, resulting in a sea breeze. In the study area the sea breeze flows over the supposed pollution source at the Mineral Separation Plant transporting the pollutants and depositing them downwind in an eastern direction.. 17.

(24) 1.5.1 Wind pattern The wind pressure gradients are the driving force for air movements. However, the wind pattern is influenced by many factors on the earth surface, causing it to differ from original predictions. These factors include topography, seasonal and diurnal variations in surface heating, changes in surface heating as determined by ground cover and proximity of large water bodies (Torvela 1994). Wind is one of the environmental forces that influence plant growth (Begon et al. 1996). Ecologically, the westerly sea breeze (Appendix 2) and the frequent warm dry berg wind play an important role in the arid coastal system (Desmet 1996) of which the present study area forms a part. Determination of the actual wind movement has been crucial to the setting of the transects and permanent sample plots in the study area. Wind direction, frequency, velocity and mist content have a direct influence on the effect of the acidic gaseous emissions from the Mineral Separation Plant fume stacks on the surrounding vegetation. The weather data used to summarise the wind factors (Figure 1.4) were obtained from the Namaqualand Sands Mining, weather station 3, located at S 31o28.14', E18o08.02' at 58 m above sea level (Struthers and Watt 2001). The recording of weather information at this station dates back to March 1991. 18.

(25) Figure 1.4: Wind rose for winter, autumn, summer and spring for 2000/2001. The isoclines (concentric circles labelled 4, 8, 12, etc) in the wind rose represent the percentage of observed records at that particular wind speed over the monitoring period. (source: Struthers and Watt 2001). 19.

(26) Severe ecological pressures in the ecosystem, emanating from wind forces and contents, precipitation levels, soil characteristics and plant competition determine the plant species that can grow in a given area. The Namaqualand coastal area experiences one of the most forceful wind regimes in the world (Mahood 2003). The prevailing wind in the present study area provides stress factors that only well adapted plant species can withstand. These plant species have morphological characteristics with ruderal or stress-tolerant strategies, to survive the harsh conditions (Vadal 1999). Prevailing winds that blow parallel to the coast, have less influence on the ecosystem of the study area, than frequent onshore westerly (Appendix 2) and off-shore easterly winds (Evenari et al. 1985). The critical winds for pollution are the stronger winds particularly those that occur during dry episodes, such as the northeasterly pre-frontal berg winds (generally north-east changing to north-west) and the strong summer winds (generally east and south winds) (Boucher 1988). There is an increase in pollution concentration in areas of stable wind regimes as compared to places with strong wind regimes (Raga et al. 1999). The strong winds provide a dilution effect on the pollutants, reducing the negative impact on the ecosystems.. Wind is an important agent in the transportation of potential pollutants from the Mineral Separation Plant into the surrounding environment. The rapid mixing and dispersal of pollutants are facilitated by the atmospheric turbulence (Boeker and Van Grondelle 1995). At the present study area, it is anticipated that the gaseous emissions will be deposited to the immediate east of the Mineral Separation Plant, because the frequent on-shore westerly winds have an influence in that direction. (Figure 1.4). The diurnal fog which rolls in the study area from the west has the potential effect of transporting mist and dust with high pollutant concentrations.. 1.5.2 Temperature and rainfall The Succulent Karoo lies in a transition zone between the Namib Desert to the north and the Cape Mediterranean-type climate to the south and receives an average of 160 mm of rainfall per year, which increases from north to south (Mahood 2003). According to De Villiers et al. (1999) rainfall, sea fog and dew amounts to a cumulative average annual precipitation of 282 mm per annum in the region, measured over a four-year period in the region.. 20.

(27) 1.6 Vegetation of the study area The Succulent Karoo Biome (Figure 1.5), is so-named due to the large variety of unique succulent plant species that dominate the area. Plants that conspicuously store water in there organs are commonly referred to as succulents (Von Willert et al. 1990). The main morphological feature of a true succulent is its storage organs (leaves, stems or roots), which allow the plant to survive dry periods, when ground water is no longer available to the roots (Van Jaarsveld et al. 2002). The Karoo flora contains an astounding variety of growth forms, and the plants thereof range widely in size, shape, type and degree of succulence, leaf consistency and persistence, thorniness, woodiness and below ground structure (Midgley and Van der Heyden 1999). As we analyse the effects of the gaseous emissions on the Karoo flora, the national, regional, and international importance of this vegetation must be considered.. Figure 1.5: The Succulent Karoo Biome in relation to other biomes of South Africa. (Source: Department of Environmental Affairs and Tourism). 21.

(28) The study area falls within the Succulent Karoo Biome. The biome has International recognition, due to the diversity of plant life in the ecosystem. Despite the small size of the biome (351,100 km2), the Succulent Karoo contains more than 30% of the World’s succulent species. This feature makes the area a unique biome of global importance (Esler et al. 2002). There are 4,949 plant species, of which 1,940 are endemic to the Succulent Karoo (Cowling and Hilton 1999). Biodiversity hotspots have been considered at global level as geographic regions of conservation priority based on the criterion that these regions consist of exceptional numbers of endemic species packed within relatively small areas that face significant threats of habitat loss (Myers et al. 2000).. The pilot study area falls within the Namaqualand Strandveld (Figure 1.6) that has been classified as Inland Tall Strandveld (Boucher and Le Roux 1989). The strandveld vegetation as a whole occupies an area of 3,817 km2, within the sandy western coastal plains that are dominated by scattered leaf succulent and drought-deciduous shrubs (Low and Rebelo 1996). The vegetation of the area is highly influenced by the interaction between the climatic and edaphic factors (Evenari et al. 1985). The present study area was used mainly for grazing purposes, before the establishment of the Mineral Separation Plant (Marx 2004 pers. Comm.). The arid winter rainfall climate of the Succulent Karoo, explains the prevalence of succulent plants and geophytes in the western part of the Biome (Desmet 1996). The winter rainfall of the Succulent Karoo is reliable and favours leaf succulents (Desmet and Cowling 1999). However, the occurrence of the extensive droughts in recent times also contributes to the stress factors that characterise the plant species distribution in the area. Clumped vegetation patterns are a dominant feature in the arid ecosystems (Eccles et al. 2001).. Marx N – Assistant Environmental Management Manager, Namakwa Sands Mine (Pty) Ltd, Saldanha.. 22.

(29) Figure 1.6: Vegetation map of the South African west coast illustrating the various vegetation types that fall within the Succulent Karoo Biome. The Namaqualand Strandveld vegetation is in light-blue adjacent to the coast and the Namakwa Sands Mineral Separation Plant falls within that locality (Mucina et al. 2005 in press).. 23.

(30) 1.7 Research objectives The pilot study was conducted for the Namakwa Sands Mine (Pty) Ltd, at their Mineral Separation Plant, with the following objectives: 1). A preliminary investigation of the surrounding vegetation to quantify the extent of potential effects of gaseous emissions from the Namakwa Sands Mineral Separation Plant.. 2). Collect baseline information about the present abundance and species composition of plant communities as well as the condition of the vegetation around the Mineral Separation Plant.. 3). Carry out an assessment to establish baseline details about the soil pH, plant foliar sulphur content, as well as the sulphate concentrations in mist and dust samples in a selected area east and south of the Mineral Separation Plant.. 4). Identify potential bioindicator plant species that can be used to detect or monitor changes in the areas around the Mineral Separation Plant that may potentially be affected by emissions, from the Mineral Separation Plant.. 5). To make recommendations that will provide Namakwa Sands Mine management with guidelines for further studies as well as possible measures for amelioration if the ecosystem is found to be negatively affected by the emissions.. 24.

(31) The pilot study will endeavour to provide preliminary information to be used in monitoring the effects of the gaseous emissions from the Mineral Separation Plant, on the adjacent Succulent Karoo vegetation. The results from the analysis of the soil pH, plant foliar sulphur content, mist and dust sulphate concentration and the selection of potential bioindicator plant species will assist in setting goals for biodiversity conservation in the ecosystem around the Mineral Separation Plant. This is an open arid ecoregion punctuated by a rugged topography (Dean and Milton 1999). Such ecological conditions can lead to unexpected influences on plant responses to environmental stimuli. Small topographic changes in the ecosystem can lead to large differences in plant community productivity (Begon et al. 1996). Quadrats could yield varying mean densities either in original or in the transformed data. What is important is the significance of the differences in the parameters being measured (Goldsmith 1991). Data that are offered in support of explanations that are free of theories are unreliable, no matter how much data happens to support them. In the absence of a theory, one could be unaware of the variables that need to be measured (Rosenzweig 1995).. We assumed that the distance from the emission source was the independent variable on which plant abundance, soil pH, electrical conductivity and SO4= concentrations depended. I tested the hypothesis that damage to plants decreases with an increase in distance from the smoke stacks. In order to infer that damage was caused by the gaseous emission pollutants, trends in pollutant concentrations were compared with trends in plant damage. Analysis of the correlation of pollutant concentrations with plant damage variables were used to draw conclusions about the effects of pollutants in the ecosystem.. 25.

(32) CHAPTER 2 LITERATURE REVIEW OF ACIDIC GASEOUS EMISSIONS AND THEIR EFFECTS ON VEGETATION _____________________________________________________________________ 2.1 Acidic gaseous emissions and their effects on vegetation The major gaseous emission by Mineral Separation Plant is sulphuric acid fumes, estimated to be 7.2 μg/m3 per second. The sulphuric acid fumes are having a negative effect on the surrounding vegetation. Evaluation of pollutants involves studying their source and the mechanism of their formation (Varney and McCormac 1971). The combustion of fossil fuels results in the emission of gaseous products, which are mainly nitrogen oxide (NOx), carbon dioxide (CO2) and water vapour (H2O). The effects, if any, of these gaseous products are not considered to be harmful in terms of the present study. Other gaseous components that are produced during the combustion or oxidation of fuels are sulphur dioxide (SO2) and oxides of nitrogen. These products emanate from the oxidation of sulphur and nitrogen that are contained in the fuels (Torvela 1994). Apparently, due to the oxidation of sulphur and nitrogen containing fuels, the gases that are produced can dissolve in water vapour present in the atmosphere to form acid rain (Brady 1990). Records of plants dying from acid rain are numerous throughout the world, especially in mountainous places where there are acid rocks and no soil buffering capacity to neutralise the acids (Ennos and Bailey 1995). Chemical pollutants cause disturbance to the ecosystem in many ways, including deposition of acid particulate matter and acid rain (Pullin 2002). At the study area the mist blown by the westerly winds dissolves the sulphur oxides from the emissions, resulting in deposition of sulphuric acid in the ecosystem. Most sulphur oxide emissions that escape into the atmosphere from the high stacks at the Mineral Separation Plant are intended to drop about 1 km away from the source. The droplets could be in the form of acid rain, depending on the vapour content in the atmosphere. Acid rain is a broad term that is used to describe several ways by which acids fall from the atmosphere (Brady 1990). A more precise term is acid deposition, which has both a wet and a dry aspect. Wet deposition refers to rain, fog, mist and snow. As this acidic water flows over and through the ground it affects a variety of plants and animals. Dry deposition refers to acidic gases and particles. About half of the acidity in the atmosphere falls back to earth through dry deposition (USEPA 2004). 26.

(33) Air pollutants that come about through anthropogenic influences such as industrial emissions, have variations in their rate of deposition, depending on the activities at the source and meteorological factors (Varney and McCormac 1971). Atmospheric emissions from industrial activities are an important factor in air pollution, especially downwind of the source (Pumure et al. 2002) (Figure 2.1). A little shift in the wind direction for 5 degrees, is sufficient to cause the concentrations at the receptor area to increase from 10%, during turbulent wind conditions, to 50% and even 90% increase during moderate to constant wind conditions respectively (Boubel et al. 1996). Lyons and Scott (1990) indicated that the dynamics of atmospheric turbulence can constantly change the pollutant concentrations and duration of action on a single receptor.. Figure 2.1: The release of acid emissions into the atmosphere from the stacks at the Mineral Separation Plant. The gaseous emissions are driven inland or east wards by the prevailing westerly winds.. 2.1.1 Sulphur dioxide as an air pollutant Sulphur dioxide and its various compounds rank highly among air pollutants that impact on the environment. Sulphur oxides are a major reason for pollution problems in many cities, although it is a non-metallic element found in nature, either free or in combination with other elements, it is almost invariably present as an impurity in coal and fuel oils that are commonly used for combustion 27.

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